Grid leak



GRID LEAK Filed August 18. 1921 WITNESSES: INVENTOR /5gg1,,, Maw/ 7Ftd/fld/Z Q I g Q4 Patented F el). 2, 1926.

- UNITED STATES PATENT. OFFICE.

HUBERT M. FREEMAN, 0F WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WEST-INGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENN-SYLVANIA.

earn LEAK.

Application filed August 18, 1921. Serial No. 493,490.

I 0 all whom it may concern:

Be it known that I, HUBERT M. FREEMAN, a citizen of the United States,and a resident of "ilkinsburg, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement in Grid Leaks,of which the following is a specification.

Hy invention relates to evacuated electric devices and more especiallyto grid leaks which may be employed in connection with such devices.

One object of my invention is to provide a grid leak which is adapted tocontrol the negative charges formed on the inner surfaces of thecontaining walls of externally controlled tubes. I

Another object of my invention is to deposit a metallic film on theinner surface of the containing walls of an externallycom trolled tube,whereby the walls of the tube may serve as a dielectric of a condenser.the opposite plates thereof being the metallic film and the externalcontrol electrode-v Other objects of my invention will be apparent fromthe following description, when taken in connection with theaccompanying drawing and claims.

-=..;,.;-.;:,During the initial evacuation of thermionic tubes and alsoduring the normal operation thereof, it has been 'found that negativeelectrostatic charges tend to accumulate upon the inner surfaces of thewalls of the tubes.

ative electrostatic charges upon the inner surface of the tube. thecharges being of such intensity that the tube ceases to function as anoscillation generator.

According to my invention. I provide means whereby the intensity of thenegatire electrostatic charges upon the inner surfaces of the walls ofthe tube may be conbe obtained, without the use of the highnnpedanceelement, by so constructing the tube as to cause the metallic deposit toserve directly as a leak between the walls of the tube opposite theelectrodes and the hot cathode.

My invention may best be understood by reference to the.accompanyingdrawing, wherein;

Fig. 1 is a diagrammatic view of an evacuated electric device embodyingmy invention, and

Fig. 2 is a cross-sectional yiew of the evacuated electric device takenon' the line I III of Fig. l.

In the accompanying drawing, I have shown my invention embodied in aspecific type of externally controlled tube, thoughv I do not wish to belimited to such an arrangement of elements.

In the drawing, 1 have shown an evacuated electric device 1 ascylindrical in form and having an anode 2 and filamentary cathodes Asmay readily be seen, such charges, in

eration and non-operation.

The plate or anode 2 is disposed longitudinally within the tube andsubstantially parallel to the plane containing the filamentary elements3, being supported by means of the conducting supports 8 and 9 which aremounted in a press 11. The stem or press As mayv readily be seen, thedesired result may also 11 is disposed in an opposite end of the tube 1to that of the press 6. The conductor 8 may extend through the press 11to serve as a terminal for the anode 2. An external control electrode12, which for purposes of illustration, has been shown as consisting ofmetallic gauze, may, if desired, completely surround the tube 1. In anyevent, it is so disposed that the filamentary cathode 3 lies in a planeintermediate the control electrode 12 and the anode 2.

A metallic film 13, which has been shown as disposed upon the innerwalls of the tube immediately adjacent the external control electrode12, may be connected, by means of a high-resistance element 14. to thefila mentary cathode 3. The metallic film 13 may be deposited upon thewalls of the tube by any means well known to the art, such, for example,as by providing extra-heavy filaments 3 and then vaporizing portionsthereof.

In the operation of my tube, it may readily be seen that the electrodes12 and 13 serve as opposite plates of a condenser with the walls of thetube functioning as a dielectric. An important advantage of such anarrangement is that it eliminates the separate grid-biasing condenserwhich 1s commonly employed in series with the gr1d to causethe grid toassume a proper negative potential. a

The main advantage of my invention,

however, resides in the provision of asim le and inexpensive grid leak,whereby the 1ntensity of the negative charges, which are formed u on theinner surface of the walls of the tu e, may be adjusted to such value asto cause most efficient operation of the tube.

While I have shown only one embodiment of my invention in the appendeddrawings, I do not wish to be limited thereby, but I desire that onlysuch restrictions shall be imposed thereon as are set forth in theappended claims.

I claim as my invention:

1. An evacuated electric device comprising an enclosing envelope, mainelectrodes forming a space-current path therein, a grid for controllingsaid space current and a grid leak contained within said envelope, saidgridleak being of a conducting material of such a resistance that theelectric flow therethrough is only sufficient to prevent theaccumulation of a s uflicient charge to interfere with the action of thedevice.

2. A three-electrode tube comprising an enclosing envelope, aspace-current path, electrodes individual to said space-current path, agrid for controlling said space-current and a grid leak, said grid leakcomprising a metallic film depositedupon the containing'walls of saidenvelope.

3. An evacuated electric device comprising an enclosing envelope, anelectrode and a grid leak contained therein, said grid leak comprising ametallic film deposited upon the containing walls of said envelope, and

r a high-resistance conductor electrically connected to said metallicfilm and to said electrode.

4. An evacuated electric device comprising an enclosing envelope, aspace-current path, electrodes individual to said space-current path, afilm of metal deposited upon predetermined portions of said enclosingenvelope and a high-resistance conductor connecting said film and one ofsaid electrodes.

5. An evacuated electric. device comprising an enclosing envelope ofnon-conducting material, a space-current path, electrodes individual tosaid space-current path, a film of metal deposited upon predeterminedportions of said enclosing envelope and a high-resistance conductorconnecting said film and one of said electrodes.

6. An evacuated electric device comprising an enclosing envelope and ahot cathode, a metallic film deposited upon the containing walls of saidenvelope and a high-resistance conductor connecting said metallic filmand said hot cathode.

7. An evacuated electric device comprising an enclosing envelope, aspace-current path, electrodes individual to said spaceeurrent path, anexternal control electrode and a co-operating internal control electrodecomprising a metallic film deposited upon the inner surface of the tube,said control electrodes being so disposed that the field of forceproduced thereby is substantially parallel to said space-current path.

8. An evacuated electric device comprising an enclosing envelope, 2.space-current path, electrodes individual to said spacecurrent path, anexternal control electrode,

a co-operating internal control electrode comprising a metallic filmdeposited upon the inner surface of the tube and a high-resistanceelement electrically connecting said metallic film and one of saidfirst-mentioned electrodes.

9. An evacuated electric device comprising an enclosing envelope, aspace-current path, electrodes individual to said spacecurrent path, anexternal control electrode, a co-operating internal control electrodecomprising a metallic film deposited upon the 1nner surface of the tubeand a high-resistance clement electrically connecting said metallic filmand one of said first-mentioned electrodes, said control electrodes alsoservmg as opposite plates of a condenser.

10. A vacuum tube having a pair-of electrodes suitably disposed thereinand extending substantially parallel to the axis of said tube, anexternal control electrode disposed adjacent the walls of the tube andconcentric with the axis thereof, a metallic film deposited upon theinner surface of said tube im ediately adjacent the portions thereofcovered by said control electrode and a high-resistance element forelectrically connecting said metallic film and one of said electrodesforming a space-current path, a 10 pair of electrodes. grid forcontrolling said space current, a 11. An electronic device including mamgrid leak and means for utillzing said grid electrodes forming aspace-current path, a leak as one plate of a condensive coupling gridfor controlling said space current, a between said grid leak and saidgrid. grid leak and means for utilizing said grid In testimony whereof,I have hereunto 15 as one plate of a condensive coupling besubscribed myname this 16th day of Autween said rid and said grid leak. gust 1921.

12. An eectronic device including main HUBERT M. FREEMAN.

